1. Field of the Invention
The present invention relates to an electronic endoscope system that adjusts a black balance of an image signal.
2. Description of the Related Art
An endoscope system is composed of a video-processor, and a video-scope and a monitor that are connected to the video-processor. The video-scope is provided with an imaging device (for example, a CCD) on a tip portion thereof. The imaging device generates image signals corresponding to an optical image that is formed at the tip portion, and the image signals are output on the monitor as the moving image, after image processing at the video-processor.
The endoscope can be attached to or removed from the video-processor easily, and several types of the video-scope can be attached to the video-processor. The characteristic of the imaging device is different according to the type of the video-scope; therefore, the black balance of the image signals that are input to the video-processor is different according to which type of the video-scope is attached thereto.
Conventionally, the black balance adjustment is conducted in the video-processor using a black balance value in order to maintain an appropriate black balance of the image signals. Because the characteristics of the image device are different according to the type of the video-scope, the black balance value needs to be recomputed whenever the type of the attached video-scope is changed.
However, the tip portion of the video-scope needs to be blacked out by a shading instrument when the black balance value is calculated. Therefore, it leaves the complicated work to the user when the type of the attached video-scope is changed.
In order to eliminate the complicated work, the black balance values regarding the several types of video-scope are stored in the memory in the video-processor, and the black balance value is read from the memory according to the type of the attached video-scope, as shown in Japanese Unexamined Patent Publication (KOKAI) NO. 11-197103. In this system, the black balance value is automatically set up according to the type of the attached video-scope.
However, the black balance of the image signal may be different according to the temperature in the operation room where the video-scope is used, or the degree of deterioration of the light source for illuminating an object, even if the same type of video-scope is attached to the same video-processor. Therefore, the black balance cannot be correctly adjusted if the black balance value is set only based on the type of the video-scope.
Recently, the auto fluorescent endoscope system has been put to practical use. In this system, a lesion, such as one of cancer, in an organ is identified by the auto-fluorescence, which the tissue emits when excitation light is illuminated thereto. The auto-fluorescence which the tissue emits is very weak; therefore, the image signal based on the auto-fluorescence needs to be amplified before it is displayed on the monitor. Due to amplification, the auto-fluorescent image that is displayed on the monitor is greatly influenced by a small change in black balance. Accordingly, it is necessary more precisely to adjust the black balance of the auto-fluorescent image than the black balance of a normal image.